The methods described facilitate high-throughput assays through multiplexing assays that until now have largely been performed individually. The principal, but not exclusive, target of the method is to provide for the evaluation of agonists and antagonists to phosphorylation (kinase) and dephosphorylation (phosphatase), as these are targets for pharmaceutical drug discovery applications.
Overall there are no less than 20 platform technologies available (for example, Radioactivity, Fluorescence Polarization, Time Resolved Fluorescence, Fluorescence Resonance Energy Transfer1, etc.), however most display important limitations for the development of a coherent screening-profiling platform. Well known drawbacks include those related to heterogeneous assay systems, limitations in ATP concentration, compound interferences and limitations of substrate size and charge. As well these methods have low level of sensitivity and are difficult to multiplex2, i.e. assay dozens of different kinases/phosphatases simultaneously. Thus there are many needs unfulfilled by the prior art, including but not limited to a need for a sensitive, robust and quantitative assay for protein post-translational modification. Further, there is a need for a multiplexed enzymatic assay that enables high throughput operation.
Among the many advantages offered by the applicant's teaching are the following: I. The assay can be applied to any type of protein kinase; II. The assay can be applied to any type of protein phosphatase; III. The assay does not exclusively rely on the use of antibodies (although some embodiments might include antibodies); IV. The methods can be used to detect and study protein kinase antagonists and agonists; V. The methods can be used to study protein kinase signal transduction cascades; VI. The methods can be used with a number of different protein kinase buffers; VII. The assay can be supplied as a kit; VIII. The assay can be used to measure activity of multiple kinases/phosphatases in cell free systems; IX. The assay can be used to determine activity of multiple kinases/phosphatases in cellular lysates; X. The assay can be used to determine various endogenous and transfected kinase activities within intact cells.
Post-translational modifications of proteins are carried out by enzymes within living cells. Known post-translational modifications include protein phosphorylation and dephosphorylation as well as methylation, prenelation, sulfation, and ubiquitination. The presence or absence of the phosphate group on proteins, especially enzymes, is known to play a regulatory role in many biochemical pathways and signal transduction pathways. Hence together, specialized kinases and phosphatases regulate enzymatic activity.
A kinase function is to transfer phosphate groups (phosphorylation) from high-energy donor molecules, such as ATP, to specific target molecules (substrates). An enzyme that removes phosphate groups from targets is known as a phosphatase. The largest group of kinases are protein kinases, which act on and modify the activity of specific proteins. Various other kinases act on small molecules (lipids, carbohydrates, amino acids, nucleotides and more) often named after their substrates and include: Adenylate kinase, Creatine kinase, Pyruvate kinase, Hexokinase, Nucleotide diphosphate kinase, Thymidine kinase.
Protein kinases catalyze the transfer of phosphate from adenosine triphosphate (ATP) to the targeted peptide or protein substrate at a serine, threonine, or tyrosine residue. Protein kinases are distinguished by their ability to phosphorylate substrates on discrete sequences. Commercially available kinases can be in the active form (phosphorylated by supplier) or in the inactive form and require phosphorylation by another kinase.
A protein phosphatase hydrolyses phosphoric acid monoesters at phosphoserine, phosphothreonine, or phosphotyrosine residue into a phosphate ion and a protein or peptide molecule with a free hydroxy group. This action is directly opposite to that of the protein kinase. Examples include: the protein tyrosine phosphatases, which hydrolyse phospho-tyrosine residues, alkaline phosphatase, the serine/threonine phosphatases and inositol monophosphatase.